The present invention relates to copolymers and terpolymers formed by the free radical initiated polymerization of either 4,7-dihydro-1,3-dioxepins or 6,7-dihydro-1,3-dioxepins with a maleic anhydride or a maleimide or a mixture of them.
The present invention further relates to the method of making these copolymers.
Furthermore, the present invention relates to the formation of a polylactone having, for example, the following general formula: ##STR2## which can be formed from certain of the copolymers mentioned above.
The copolymers and terpolymers of the present invention are useful as epoxy resin modifiers and curing agents. The resulting systems are useful as coatings, adhesives and other applications.
Dioxepins are useful as solvents. Therefore, a polymer formed from a dioxepin and one or more additional monomers would be expected to possess the advantageous characteristic of improving the compatability of the additional monomer with respect to a third moiety. This would also provide the physical advantages of putting the additional monomers in a polymer. Thus, when the additional monomers were used in any type of coating application using the polymer of the present invention, it would be expected to improve the strength of the coating.
Finally, dioxepin is dermatologically safe. Therefore, a copolymer formed from dioxepin and a second dermatologically safe monomer would presumably provide a dermatologically safe copolymer.
The problem is to copolymerize or terpolymerize dioxepin. U.S. Pat. No. 3,385,832 discloses a copolymer formed from trioxane and dioxepin. But the dioxepin ring is broken in the formation of the polymer. U.S. Pat. No. 3,280,148 discloses a bis-dioxepin and broadly states that this monomer is copolymerizable with vinyl monomers. Sterling U.S. Pat. No. 3,219,629 discloses a copolymer of certain vinyl monomers and 1,3-dioxepins. However, the polymers do not contain a high percentage of the dioxepin moiety in the polymer. In fact, in these systems, the dioxepin acts as a chain transfer agent, thereby limiting the size of the polymer. As the concentration of dioxepin is increased, the reaction is decreased and the size of the polymers being formed is also decreased.
Dioxepin does not copolymerize readily with typical vinyl monomers, particularly with any substantial amount of the dioxepin moiety. In fact, dioxepin does not even homopolymerize. Therefore, it is unexpected for dioxepin to copolymerize. But, according to the present invention, dioxepin does copolymerize with certain electron-accepting monomers to form a copolymer containing approximately 50 mole percent dioxepin. These electron-accepting monomers comprise maleic anhydrides and maleimides. Thus, it has been discovered, contrary to these indications, that 1,3-dioxepins copolymerize with maleic anhydride or a maleimide, thus allowing a copolymer with the characteristics of a maleic anhydride or maleimide combined with the benefits of the dioxepin, i.e., the increased compatability and dermatological safety.
The copolymer formed with maleic anhydride can further be rearranged to form a polylactone. The most important of these polylactones is shown below (I): ##STR3## This polymer itself is useful as an epoxy curative and generally as a modifier in polyblends.